The primary objectives of this project are to purify one or more of the heat-labile E. coli enterotoxins and to characterize it physicochemically and immunochemically. Of special interest is whether more than one species of E. coli enterotoxin exists and what its relationship is to other E. coli and other bacterial enterotoxins. We have established the optimal conditions for production of the enterotoxin and for its elution from ion-exchange columns. Under these conditions, the enterotoxin is found to be the first of four proteins eluted from the column and is a larger molecular weight, slow moving protein by acrylamide gel analyses. Our future work will be focused on the continued purification and isolation of one or more enterotoxins, followed by its biochemical characterizations. With the availability of pure enterotoxin, studies concerned with delineating its molecular mechanisms of action, and the development of assays even simpler than the adrenal cell system, will be possible.